Steady-State Visual Evoked Potentials Can Be Explained by Temporal Superposition of Transient Event-Related Responses

<p><b>Background:</b> One common criterion for classifying electrophysiological brain responses is based on the distinction between transient (i.e. event-related potentials, ERPs) and steady-state responses (SSRs). The generation of SSRs is usually attributed to the entrainment of a neural rhythm driven by the stimulus train. However, a more parsimonious account suggests that SSRs might result from the linear addition of the transient responses elicited by each stimulus. This study aimed to investigate this possibility.</p> <p><b>Methodology/Principal Findings::</b> We recorded brain potentials elicited by a checkerboard stimulus reversing at different rates. We modeled SSRs by sequentially shifting and linearly adding rate-specific ERPs. Our results show a strong resemblance between recorded and synthetic SSRs, supporting the superposition hypothesis. Furthermore, we did not find evidence of entrainment of a neural oscillation at the stimulation frequency.</p> <p><b>Conclusions/Significance:</b> This study provides evidence that visual SSRs can be explained as a superposition of transient ERPs. These findings have critical implications in our current understanding of brain oscillations. Contrary to the idea that neural networks can be tuned to a wide range of frequencies, our findings rather suggest that the oscillatory response of a given neural network is constrained within its natural frequency range.</p&gt

On the role of neuronal oscillations in auditory cortical processing

Although it has been over 100 years since William James stated that everyone knows what attention is , its underlying neural mechanisms are still being debated today. The goal of this research was to describe the physiological mechanisms of auditory attention using direct electrophysiological recordings in macaque primary auditory cortex (A1). A major focus of my research was on the role ongoing neuronal oscillations play in attentional modulation of auditory responses in A1. For all studies, laminar profiles of synaptic activity, (indexed by current source density analysis) and concomitant firing patterns in local neurons (multiunit activity) were acquired simultaneously via linear array multielectrodes positioned in A1. The initial study of this dissertation examined the contribution of ongoing oscillatory activity to excitatory and inhibitory responses in A1 in passive (no task) conditions. Next, the function of ongoing oscillations in modulating the frequency tuning of A1 during an intermodal selective attention oddball task was investigated. The last study was aimed at establishing whether there is a hemispheric asymmetry in the way neuronal oscillations are utilized by attention, corresponding to that noted in humans. The results of the first study indicate that in passive conditions, ongoing oscillations reset by stimulus related inputs modulate both excitatory and inhibitory components of local neuronal ensemble responses in A1. The second set of experiments demonstrates that this mechanism is utilized by attention to modulate and sharpen frequency tuning. Finally, we show that as in humans, there appears to be a specialization of left A1 for temporal processing, as signified by greater temporal precision of neuronal oscillatory alignment. Taken together these results underline the importance of neuronal oscillations in perceptual processes, and the validity of the macaque monkey as a model of human auditory processing

Is auditory discrimination mature by middle childhood? A study using time-frequency analysis of mismatch responses from 7 years to adulthood

Behavioural and electrophysiological studies give differing impressions of when auditory discrimination is mature. Ability to discriminate frequency and speech contrasts reaches adult levels only around 12 years of age, yet an electrophysiological index of auditory discrimination, the mismatch negativity (MMN), is reported to be as large in children as in adults. Auditory ERPs were measured in 30 children (7 to 12 years), 23 teenagers (13 to 16 years) and 32 adults (35 to 56 years) in an oddball paradigm with tone or syllable stimuli. For each stimulus type, a standard stimulus (1000 Hz tone or syllable [ba]) occurred on 70% of trials, and one of two deviants (1030 or 1200 Hz tone, or syllables [da] or [bi]) equiprobably on the remaining trials. For the traditional MMN interval of 100–250 ms post-onset, size of mismatch responses increased with age, whereas the opposite trend was seen for an interval from 300 to 550 ms post-onset, corresponding to the late discriminative negativity (LDN). Time-frequency analysis of single trials revealed that the MMN resulted from phase-synchronization of oscillations in the theta (4–7 Hz) range, with greater synchronization in adults than children. Furthermore, the amount of synchronization was significantly correlated with frequency discrimination threshold. These results show that neurophysiological processes underlying auditory discrimination continue to develop through childhood and adolescence. Previous reports of adult-like MMN amplitudes in children may be artefactual results of using peak measurements when comparing groups that differ in variance

Behavioral and Electrophysiological Measures of Speech-in-Noise Perception in Normal Hearing and Hearing Impaired Adults

University of Minnesota Ph.D. dissertation. July 2017. Major: Speech-Language-Hearing Sciences. Advisors: Dr. Yang Zhang, Dr. Peggy B. Nelson. 1 computer file (PDF): vii, 161 pages.Understanding speech in background noise is difficult for many individuals. Mechanisms responsible for variability in speech-in-noise performance across individuals are not well understood. Electrophysiological measures allow for an examination of the timing and strength of neural responses to speech along the auditory pathway and can be used to explore mechanisms underlying reduced speech perception in noise. This dissertation used behavioral and electrophysiological measures to examine the effects of background noise on the neural coding of speech and to identify potential neural correlates of speech perception in individuals with and without hearing impairment. N1-P2, mismatch negativity (MMN), and P3 auditory event-related potentials (AERPs) and associated event-related cortical oscillations in various frequency bands of interest were collected in response to syllable-level stimuli in noise. Behavioral measures consisted of phoneme discrimination and sentence recognition in noise. Results indicated that in addition to impacting averaged AERP responses, background noise disrupted cortical oscillatory rhythms in response to speech in frequency bands of interest across participants. Results also showed that the effects of background noise and hearing impairment on the neural coding of speech are different at different levels of cortical processing. This work revealed that AERPs and associated cortical oscillations represent potential neural correlates of speech perception in noise in individuals with and without hearing impairment. These findings have potential theoretical and practical implications regarding the use of electrophysiological measures for the assessment and rehabilitation of communication difficulties in background noise

Disrupted auditory N1, theta power and coherence suppression to willed speech in people with schizophrenia

The phenomenon of sensory self-suppression - also known as sensory attenuation - occurs when a person generates a perceptible stimulus (such as a sound) by performing an action (such as speaking). The sensorimotor control system is thought to actively predict and then suppress the vocal sound in the course of speaking, resulting in lowered cortical responsiveness when speaking than when passively listening to an identical sound. It has been hypothesized that auditory hallucinations in schizophrenia result from a reduction in self-suppression due to a disruption of predictive mechanisms required to anticipate and suppress a specific, self-generated sound. It has further been hypothesized that this suppression is evident primarily in theta band activity. Fifty-one people, half of whom had a diagnosis of schizophrenia, were asked to repeatedly utter a single syllable, which was played back to them concurrently over headphones while EEG was continuously recorded. In other conditions, recordings of the same spoken syllables were played back to participants while they passively listened, or were played back with their onsets preceded by a visual cue. All participants experienced these conditions with their voice artificially shifted in pitch and also with their unaltered voice. Suppression was measured using eventrelated potentials (N1 component), theta phase coherence and power. We found that suppression was generally reduced on all metrics in the patient sample, and when voice alteration was applied. We additionally observed reduced theta coherence and power in the patient sample across all conditions. Visual cueing affected theta coherence only. In aggregate, the results suggest that sensory self-suppression of theta power and coherence is disrupted in schizophrenia.Oren Griffiths, Bradley N. Jack, Daniel Pearson, Ruth Elijah, Nathan Mifsud, Nathan Han, Sol Libesman, Ana Rita Barreiros, Luke Turnbull, Ryan Balzan, Mike Le Pelley, Anthony Harris, Thomas J. Whitfor

Cortical activations underlying human bipedal balance control

Human bipedal balance is a complex sensorimotor task controlled by the central nervous system. Balance impairments, caused by aging or neuromuscular diseases, often lead to falls which are one of the leading causes of injury and subsequent increases in health care costs. Hence, understanding the mechanisms underlying human bipedal balance control has many functional and clinical implications. Traditionally, it was believed that balance control is mediated by subcortical structures. However, evidence from research in the past few decades has shown that the cerebral cortex plays a major role in bipedal balance control. Nevertheless, the cortical contributions in balance control are still unclear. Hence, the purpose of this thesis was to extend the understanding of cortical involvement in human bipedal balance control. Specifically, the two overarching goals of this thesis were to examine evidence of a cortical network involvement and its generalizability across reactive and predictive balance control. These two overarching goals were addressed through four different studies. Study 1 explored the frequency characteristics and mechanisms underlying the generation of perturbation-evoked potentials. Study 2 investigated cortical activity linked to ‘automatic’ balance reactions that occur continuously while standing still and its dependence on the amplitude of these balance reactions. Study 3 examined the cortical activations related to the preparation and execution of anticipatory postural adjustments that precede a step and whether the activations are dependent on the context of control. Study 4 was designed to examine the functional connectivity in balance control and whether similar networks underlie reactive and predictive balance control. Studies were conducted on young healthy adults and cortical activations were acquired using electroencephalography during feet-in-place balance reactions, standing still, and voluntary stepping. Overall, the findings of these studies provided direct and indirect evidence for the involvement of a cortical network in balance control and its generalizability across different classes of balance control. This work reinforces the view that cortical networks likely play an important role in the control of stability. It is proposed that the synchronized activation of neural assemblies distributed across the cortex might have contributed to the balance-related cortical activations. The findings of this thesis extend the understanding of cortical control of human bipedal balance that may help to inform future, more precise models of the cortical contributions to balance control. This, in turn, can inform future diagnostic and therapeutic approaches to improve mobility among those with balance impairments

Electrophysiological and behavioural consequences of cross-modal phase resetting

No abstract available